How long after vaccination does the body develop immunity to the H1N1 2009 virus?
Adults can expect to develop immunity by two weeks after receiving the vaccine . However, a child below the age of 10 will need two doses of the H1N1 vaccine, spaced about a month apart, and will not develop immunity until up to two weeks after the second dose. Younger children need two doses because they have had limited exposure to influenza viruses and do not have preexisting antibodies.
